Note: said society is preindustrial and has ample access to flowing water, but not fossil fuels or radioactive deposits. It also has access to mountain hot springs, which I thought could also be used as “batteries” during times when streams freeze. This last point is what set him off.
He also really hates wind turbines.
I’m not sure I’m getting what you mean by the hot spring winter battery thing. Frozen water at the top of an incline definitely has stored kinetic energy but warming it up enough to capture that energy would probably not be worth it, unless I’m completely misunderstanding what you have in mind.
edit: oh wait do you mean that they have the hot springs behind a dam that they open when other waters freeze? I could see that happening but the question is how warm would the reservoir be and how far could the water flow before freezing. The water at the origin would have to be pretty warm, ie very close to magma vents, on order to stay melted long enough to flow any meaningful distance.
The hot springs act as reservoirs, allowing the civilization to have a (reduced, of course) supply of liquid water during cold seasons. The water is passively heated by magma currents running underneath (akin to how hot springs generally form) so they don’t have to expend any additional energy to warm it.
It’s like a damn Jacuzzi. The civilization pretty much has on-demand hot baths.
Not sure if you were planning on using it as such (or how much you care) but hot spring water can’t be used for drinking water, at least not for any length of time.
It’s just for powering machines.